摘要:

On the basis of the analysis of approximately 3000 high spectral resolution scans of the direct absorption of sunlight by atmospheric sodium atoms the average seasonal and diurnal variations of atomic sodium abundance in the upper atmosphere have been deduced for Madison, Wisconsin (43°4.5′N, 80°24.3′W). For the period 1971–1974 an average maximum abundance of 7.7 × 109atoms/cm² was observed to occur in early March and an average minimum of 2.9 × 109atoms/cm² in late August. The abundance at local noon relative to the abundance ±4½ hours away from noon averaged 2.3 for the period of January and February and between 1.3 and 1.7 for the remainder of the year, with the minimum in June. The diurnal abundance variation in the winter appears to show a correlation with snow cover, suggesting a relationship with changes in the e

ISSN:0148-0227    

DOI:10.1029/JA082i019p02607

年代:1977

数据来源: WILEY

摘要:

Recent laboratory measurements of the molecular oxygen photoabsorption cross section at a temperature of 195 K provide a more suitable basis for the determination of mesospheric molecular oxygen densities than previously available room temperature cross sections. The 195 K cross sections have been used to analyze the data from 34 rocket measurements of the atmospheric extinction of solar Lyman α radiation. Observations from Woomera (31°S) are compared with those from other locations (mainly 35° and 59°N), and separate mean molecular oxygen density profiles are derived for each of the three latitudinal groups. Averaging the data from the flights at all locations yields an observational mean molecular oxygen density profile which exceeds the mean Cira (1972) model by about 20% at 70 km and by about 9% at 90 km. Part of this difference may be due to residual effects on the cross section of temperature variations in the 70‐ to 90‐km region. Absorbers other than molecular oxygen probably account for a major part of the remaining difference between the observations and the model, and further refinement of the Lyman α extinction technique will require a more accurate estimate of these cor

ISSN:0148-0227    

DOI:10.1029/JA082i019p02613

年代:1977

数据来源: WILEY

摘要:

Ion composition at mesospheric altitudes has been measured at and compared between high‐ and mid‐latitude sites under summer daytime conditions. Both rocket‐borne measurements were made with pumped quadrupole ion mass spectrometers (mass range, 15–145 amu). Apogee occurred below 90 km on each flight, subsonic sampling near the mesopause thus being possible. Water cluster dissociation was further minimized by using low attractive bias potentials of —5 V for each instrument. The mid‐latitude data were obtained at Wallops Island, Virginia (latitude, 37.8°N; longitude, 75.5°W), on June 30, 1973, at 1510 LMT (χ = 43°). Large quantities of hydronium cluster ions were observed through 109+, with maximum concentrations at 55+and 73+. Also cluster ions of nitric oxide were observed through 84+. The high‐latitude launch occurred at Kiruna, Sweden (latitude, 67.9°N; longitude, 21.1°E), on August 2, 1973, at 0700 LMT (χ = 68.5°), following visual sighting of a noctilucent cloud on the prior evening. The data near the mesopause show the typical cluster ions mentioned above but also a preponderance of heavy ions between 90 and 145 amu, with groupings 18 amu apart but unrelated to the more typical cluster ions. One possible set of consistent identifications leads to iron and iron oxide hydrates. These results may suggest the presence of metallic particulates and ions which form hydrated cluster ions wi

ISSN:0148-0227    

DOI:10.1029/JA082i019p02619

年代:1977

数据来源: WILEY

摘要:

The fundamental diurnal component of temperature, composition, and wind fields is discussed for the earth's thermosphere. The results are delineated in terms of energy sources in the lower atmosphere, mesosphere, and thermosphere, illustrating that EUV is the predominant excitation source above 130 km. Diurnal variations in the composition of H, He, O, O2, and Ar are analyzed in terms of effects from thermal expansion in diffusive equilibrium—normally assumed in empirical models—and diffusion associated with chemistry, wind circulation, and exospheric flow. Next to thermal expansion, wind‐induced diffusion is the single most important process; it dominates the diurnal variations of He and prevails in the diurnal variations of O, O2, and Ar below 200 km. The wind effect is shown to eliminate isopycnic levels that develop in diffusive equilibrium solutions, and it shifts the phase of the lighter and heavier species to earlier and later local times, respectively. Exospheric flow dominates the diurnal variations of hydrogen, while winds are only important in the lower thermosphere where they increase the H amplitude by 50%. Dissociation of O2and ion chemistry are of secondary importance for O but can significantly influence the diurnal variations of O2such as by moving the phase to earlier local times. Comparison between theory and satellite data from Explorer 32, Ogo 6, San Marco, and AE‐C shows substantial agreement, with the exception of O2, which requires an additional sink during

ISSN:0148-0227    

DOI:10.1029/JA082i019p02628

年代:1977

数据来源: WILEY

摘要:

Maximum entropy spectral analysis (Mesa) of a time series consisting of 107 annual mean values of the geomagnetic activity index aa and analysis of subsets of this time series yield interesting results concerning both the maximum entropy method itself and periodicities in geomagnetic activity. The influence of removing a trend from the original data is found to have an even more drastic influence on the low‐frequency side of the spectrum than could be expected. Long‐period peaks are found for most subsets but are very unstable (40–80 years) and cannot be safely related to any physical phenomena. With data such as the aa time series, Mesa cannot provide reliable estimates of periodicities (if any) having a period exceeding one third to one half of the record length. The ‘22‐year’ solar magnetic cycle and the ‘11‐year’ solar cycle together with some of their harmonics are observed, and their stabi

ISSN:0148-0227    

DOI:10.1029/JA082i019p02641

年代:1977

数据来源: WILEY

摘要:

Using the Atmosphere Explorer satellite AE‐C, we observe large‐scale (10‐ to>200‐km) irregular biteouts of up to three orders of magnitude in the ion concentrationNiin the nighttime equatorialFregion associated with small‐scale inhomogeneities inNi. Similar phenomena were reported by Hanson and Sanatani but without the more complete plasma diagnostics present on AE. Simultaneous plasma velocity observations show irregular upward and westward motion of the order of 150 m s−1associated with some of these ‘bubbles,’ while others move more slowly or move with approximately the velocity of the background plasma. The plasma composition signatures indicate that most of the bubbles observed have recently moved upward. Several features of recent VHF radar observations can be understood as resulting from these plasma bubbles, e.g., the ‘plume’ features and very high apparent velocities seen on range‐time‐intensity spreadFmaps and the very complex and/or wide spectral features observed using such radars. Bubbles that move upward typically also move westward with respect to the background plasma. This may explain the east‐west asymmetries seen in studies of equatorial irregularities made using HF radar, HF transequatorial propagation, and detailed 6300‐Å tropica

ISSN:0148-0227    

DOI:10.1029/JA082i019p02650

年代:1977

数据来源: WILEY

摘要:

A description is given of the solar particle event of April 16, 1970, as recorded by two Vela satellites which were in the vicinity of the earth's bow shock at 18RE. Comparison with Explorer 35 in lunar orbit indicates that the early time profile of the event was due to a spatial structure convected past the earth, and the orientation of the convected front is deduced. Anisotropies and pitch angle distributions of energetic protons are obtained from a 32‐point sampling of the particle flux over the celestial sphere with a time resolution of 1 min. The net flow patterns inferred in interplanetary space reveal two reversals in the north‐south component, in general alignment with the magnetic field; neither was accompanied by a magnetic field reversal. Novel features of the pitch angle distributions recorded at proton energies of ≈ 1 MeV included (1) a narrow forward peak at 0° pitch angle observed in interplanetary space and accompanied by a smaller backscatter peak (we conclude that the forward peak is a real interplanetary effect uncontaminated by the presence of the bow shock), (2) accompanying this forward peak, a difference in the omnidirectional intensities at Vela 6B and at Vela 5B, of a factor of ≈3, when these satellites were situated in the solar wind and in the magnetosheath, respectively, (3) a pronounced depression over approximately one hemisphere which was recorded by both Vela 6B and 5B when each was in the magnetosheath and which represents a distortion of the interplanetary pitch angle distribution due to propagation of particles into the magne

ISSN:0148-0227    

DOI:10.1029/JA082i019p02657

年代:1977

数据来源: WILEY

摘要:

During the event of April 16, 1970, energetic (∼0.7 MeV) protons were observed by Vela 6B in the solar wind and by Vela 5B in the magnetosheath. During one 4‐hour period the omnidirectional flux measured by 5B was a factor of 3 larger than that measured by 6B. The pitch angle distribution observed at this time by 6B was characterized by a strong peak at 0° pitch angle. Transformation of this distribution according to the Liouville equation accounts for the enhanced omnidirectional flux and the shape of the pitch angle distributions observed at 5B. At a later time in the event, distorted pitch angle distributions, which were observed in the magnetosheath, are accounted for by a Liouville transformation of an assumed unidirectional distribution in interplanetary space. We conclude that particle entry into the magnetosheath was approximately adiab

ISSN:0148-0227    

DOI:10.1029/JA082i019p02665

年代:1977

数据来源: WILEY

摘要:

During geomagnetically quiet times, particle precipitation at low to middle latitudes (L≲ 4) results from a combination of pitch angle diffusion into the bounce loss cone and the opening of the bounce loss cone in the direction of drift to a maximum value which defines the drift loss cone. Some previous observations suggest that the pitch angle scattering of kilovolt electrons in the plasmasphere occurs in a localized region of space rather than throughout the course of their azimuthal drift. If their source is localized, quasi‐trapped particles outside of the source region precipitate into the atmosphere at a rate that can be correlated with the rate of increase of the bounce loss cone angle in the direction of drift. Source localization also affects pitch angle distributions which are characterized by the maximum loss cone encountered during the course of the particles' azimuthal drift. Patterns describing the precipitation of quasi‐trapped particles and the spatial evolution of the pitch angle distribution at a specificLvalue can be constructed for hypothetical localized sources. A simple idealized model, in which the source is represented by a delta function in space, leads to a qualitative picture of the morphology of precipitation in both northern and southern hemispheres in the two cases of a fixed magnetospheric (i.e., local time) and fixed geographic (i.e., longitude) source. The nature of mid‐latitude sources can be inferred from a comparison of observations of quasi‐trapped and precipitating particles with the characteristics predicted by these models. Some observations of pitch angle distributions of 29‐keV and 59‐keV electrons atL≈ 2 from the satellite 1972‐76B exhibit some of the features that characterize a highly localized source. These data can be interpreted as evidence of a corotating source fixed in the longitude i

ISSN:0148-0227    

DOI:10.1029/JA082i019p02671

年代:1977

数据来源: WILEY

摘要:

A simple and general method for applying the results of a microinstability analysis to models of the solar wind is described. Existing two‐fluid models are found to become unstable at heliocentric distances varying from 3 to 11RS. The development of these ‘heat conduction’ microinstabilities affects the energy and momentum transport, observable wave spectrum, cosmic ray diffusion, and properties of minor ions in the solar wind. A proposal which would rationally modify the energy transport is developed. It is suggested that the plasma fluctuations observed near the earth could largely be a result of these instabilities. The observed temperatures and velocities of helium ions can be explained qualitatively in terms of resonant interaction with the different waves which are expected to be generated under different solar wind condi

ISSN:0148-0227    

DOI:10.1029/JA082i019p02677

年代:1977

数据来源: WILEY